Meiotic effects of Robertsonian translocations in tuco-tucos of the Ctenomys perrensi superspecies (Rodentia: Ctenomyidae)

Meiotic behaviour was studied in males of the Ctenomys perrensi superspecies from Argentina that show variations in their chromosome number mostly due to Robertsonian translocations (Rb). A significant positive cor- relation between cell chiasma frequencies and total chromosome numbers was found. The reduction in chiasma fre- quency observed in individuals with Rb rearrangements occurred mainly at expenses of proximal and interstitial chi- asmata, although significant differences between Rb trivalents and bivalents both in chiasma distribution and univa- lent frequency were also observed. Nevertheless, not all changes in chiasma distributions could be ascribed to Rb re- arrangements. Chromosome synapsis was analysed in Rb hetero- and homozygotes. Trivalents showed a high frequency of synapsis at pericentromeric regions, suggesting no mechanical incompatibilities or delay in the synap- tonemal complex formation in such regions. The relationship between chiasma distributions and synaptic patterns is discussed and a hypothesis about the possible role of telocentric or subtelocentric regions in these processes is pro- posed. It is also concluded that one or two Rb translocations in heterozygosis have weak direct effects on the fertility of the male carriers; therefore C. perrensi superspecies may be prone to maintain Rb chromosomal rearrangements.